I. Field
The present invention relates generally to electromagnetic interference (EMI) circuits and protection devices. More specifically, the present invention relates to an electromagnetic interference suppression component and protection component assembly for a motor.
II. Description of Related Art
Motors, especially DC motors that utilize brushes to drive a commutator, are known to generate electrical noise (i.e., electromagnetic interference or EMI) capable of interfering with the operation of nearby electronic equipment. To alleviate EMI problems, the motors may be fitted with various types of filters specifically configured to reduce the EMI to acceptable levels.
FIG. 1 illustrates a schematic diagram of a motor assembly 100 that includes an EMI filter circuit that may be electrically coupled to a motor 115 to reduce EMI generated by the motor 115. The EMI filter circuit includes a pair of capacitors 107ab and a pair of coils or chokes 111ab that together cooperate to suppress or reduce the EMI noise generated by the motor 115.
In addition to EMI filter circuits, the motor assembly 100 may include various protection components 105 and 109 to protect the motor 115 against over current conditions, over-heating, over voltage, etc. For example, a protection device, such as polymeric positive temperature coefficient (PPTC) device 109, bi-metal device, thermal cutout (TCO) device, etc., may be inserted in series with a power lead of the motor 115. The PPTC component 109 may correspond to a non-linear device with a resistance that changes in relation to the temperature of the PPTC component 109. The bi-metal device and thermal cutout device may include a pair of metal strips in contact with one another that separate above a set temperature. The bi-metal device may be resettable type of fuse device, whereas the thermal cutout device may be a single shot device (i.e., a non-resettable fuse device). A varistor 105 may be inserted in parallel with the power leads of the motor 115. The varistor 105 may be utilized to protect against excessive transient voltages that might damage the motor 115.
During the manufacturing process of the motor assembly 100, the various components discussed above are connected together via leads of various lengths to form the circuit illustrated in FIG. 1. The assembled components may then be inserted into a metal motor housing. Ground nodes illustrated in the schematic may be electrically coupled to the motor housing.
One problem with this approach is that the leads between the various components tend to act as antennae, which exacerbates EMI issues. Accordingly, noise generated by these leads has to be taken into consideration in the selection of values for the capacitors 107ab and chokes 111ab. 
In addition, assembling the various components may be complex, especially for small motor housings that provide very confined spaces for placement of the components. This complexity increases assembly time and the likelihood of manufacturing defects. This, in turn, necessarily increases manufacturing costs of the motor assembly.
Other problems with existing motor assemblies will become apparent in view of the disclosure below.